Host Defense

How macrophages build a wall

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Science  11 Nov 2016:
Vol. 354, Issue 6313, pp. 717-718
DOI: 10.1126/science.354.6313.717-b

Granulomas are a defining feature of infection with Mycobacterium tuberculosis, the causative agent of tuberculosis. Macrophages are the primary component of these cell structures, which are thought to protect the host by walling off the pathogen. Cronan et al. studied granulomas in optically transparent zebrafish infected with M. marinum to directly visualize how they form. They observed that macrophages in granulomas undergo epithelial reprogramming, up-regulating many molecules and adhesion structures characteristic of epithelial cells. Disrupting this process by blocking E-cadherin, a protein that drives the epithelialization process, led to granulomas with a disorganized appearance. Unexpectedly, however, this reduced the fishes' bacterial burden, suggesting that granulomas may not always be host-protective.

Immunity 45, 861 (2016).

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